1. Field of the Invention
The present invention relates to a blanket-to-blanket printing unit for a web-fed rotary printing press, in which each of the plate cylinders is individually driven by an associated drive motor and in which the blanket cylinders are mechanically coupled to each other and are driven by one common drive motor. In particular, the present invention relates to a printing unit for a web-fed rotary printing press for printing newspapers, in which each of the blanket cylinders carries a sleeve shaped printing blanket
2. State of the Art
In a lithographic web-fed rotary printing press, a running paper web is usually fed through a plurality of blanket-to-blanket printing units, which apply a multi color image to both sides of the web. For driving the printing units, there are different known kinds of drive systems and drive principles from the prior art.
One of the most common driving principles which is used in most of today's web-fed rotary printing presses employs a longitudinal drive shaft which is coupled to a main drive of the printing press and which drives each blanket-to-blanket printing unit via a bevel gear respectively. The bevel gear is connected to a gear train of the respective printing unit, which includes the meshing drive gears of the upper and lower plate cylinders and their associated blanket cylinders.
DE 41 38 479 A1 of "Baumueller" describes a blanket-to-blanket printing unit in which each of the upper and lower plate- and blanket cylinders is driven independently by an own electric motor, without providing a mechanical coupling between the cylinders. Owing to a differential motion between the upper and the lower blanket cylinders of the of the printing unit, which could occur in case of web-fed printing presses having blanket cylinders with sleeve-shaped printing blankets, register errors and print defects are likely to occur. Furthermore, the use of one individual electric motor for each of the cylinders of the printing unit requires a highly sophisticated control and regulating electronics, in order to avoid misregistering of the images particularly at high press speeds.
EP 0 64 44 048 A2 purports to disclose a blanket-to-blanket printing unit for a web-fed rotary printing press, in which the upper plate cylinder and its associated upper blanket cylinder are mechanically coupled via a first gear train and are driven by a first electric motor via a first gear box. The lower blanket cylinder and its associated lower plate cylinder are mechanically coupled via a second gear train and are driven by a second electric motor via a second gear box. The document further describes a satellite printing unit in which the central impression cylinder is driven by a first electric motor and in which the plate- and blanket cylinders of each satellite printing couple are mechanically connected via a gear train and are driven independently by an associated own electric motor. Each of the electric motors for driving the printing couples is mechanically connected to the respective blanket cylinder of the couple, in the same way as the printing unit of DE 41 38 479 A1, the printing units described in EP 0 64 40 48 A2 may also be subject to register errors and print defects, which are caused by the creeping of the printing blankets on the first and second blanket cylinders of each printing unit when employing cantilevered blanket cylinders carrying sleeve-shaped printing blankets.
JP 63-236651 purports to disclose a blanket-to-blanket printing unit for a web-fed rotary printing press, in which an upper blanket cylinder and an associated upper plate cylinder are for driving purposes connected via a first gear train and in which a lower blanket cylinder and an associated lower plate cylinder are connected for driving purposes via a second gear train. A first motor drives the upper plate cylinder and a second motor drives the lower blanket cylinder. The apparatus described in JP63-23661 is also likely to cause register problems and print defect when employing blanket cylinders with sleeve-shaped printing blankets.